1. Field of the Invention
The invention relates to a cooling structure for a rotary electric machine, and more particularly, to a cooling structure for a rotary electric machine, that uses coolant to cool coil end portions of a stator coil.
2. Description of Related Art
A rotary electric machine that includes a stator provided with a plurality of stator coils (hereinafter simply referred to as “coils” where appropriate) arranged in the circumferential direction on an inner peripheral portion of a cylindrical stator core is known. These coils are wound around teeth that are formed protruding radially inward on the inner peripheral portion of the stator core, and include coil end portions in which both end portions of the coils protrude to the outside at both ends of the stator in the axial direction.
Each coil is connected to a lead wire, and current flows to the coil by applying voltage from an external source via this lead wire. At this time, so-called copper loss due to electrical resistance occurs at the inner portion of conductive wire such as copper wire that is covered with insulation, for example, and used to form the coils. As a result, the coils generate heat. This heat causes the coil temperature to rise, and when the coil temperature rises, the insulating performance of the coils decreases. When the rotary electric machine is a polyphase alternating current (AC) motor, discharge tends to occur particularly between coil end portions of different phase coils where the potential difference is large.
In order to prevent this kind of discharge, the coil end portions of the coils are cooled by coolant such as cooling oil, for example. Japanese Patent Application Publication No. 2006-271150 (JP-A-2006-271150) describes one such related art.
JP-A-2006-271150 describes a cooling structure for a motor-generator. In this cooling structure, the coil end portions that protrude in a generally annular shape toward the outside at the axial end surfaces of the stator core are covered in a fluid-tight manner by a cooling jacket. Cooling oil is supplied so as to flow inside the jacket, such that the coil is cooled by the entire coil end portions contacting the cooling oil in the circumferential direction. Also, with this cooling structure, the stator is housed inside a cylindrical case, and a side plate is attached to each side of this case in the axial direction. An oil supply port is formed in the side plate and the cooling jacket, and an oil supply port is formed in each side in the axial direction, corresponding to the coil end portions at both ends in the axial direction.
With the cooling structure in JP-A-2006-271150, an oil supply port is provided in the cooling jacket provided on each side of the stator in the axial direction, such that cooling oil is supplied from these oil supply ports to the coil end portions on both sides in the axial direction.
However, one coil end portion to which a lead wire for supplying power to the stator coil is electrically connected, i.e., the lead side coil end portion, differs in size (i.e., the length in the axial direction and/or the width in the radial direction) and shape from the other coil end portion positioned on the opposite side in the axial direction, i.e., the non-lead side coil end portion. In particular, when the stator coil is a so-called segment coil in which a generally spiral-shaped coil is formed by a plurality of two leg portions of conductive wires bent in a general U-shape being arranged in the radial direction and inserted into slots straddling the teeth of the stator core from one side in the axial direction, and the two leg portions that are protruding outward from the other end side in the axial direction being sequentially connected to the leg portions of the adjacent conductive wires, the lead side coil end portion tends to be formed larger than the non-lead side coil end portion.
In this case, when an oil chamber is formed for each coil end portion on both sides in the axial direction using the cooling jacket of a similar shape and cooling oil is supplied into each oil chamber from the oil supply ports provided on both sides in the axial direction, the pressures and amounts of cooling oil supplied to the oil chambers may become uneven due to a difference in the size of the coil end portions or the like. As a result, even cooling performance, and thus insulating performance, in the coil end portions may not be able to be obtained.
Also, with the cooling structure in JP-A-2006-271150, two oil supply ports are formed opening toward opposite sides in the axial direction. Therefore, when attempting to connect oil supply pipes to the oil supply ports formed pointing in opposite directions as described above when assembling a motor-generator as a power supply for running that incorporates this cooling structure to a transmission, the assembly posture, the assembly space, and the work space and the like of the motor-generator may make it difficult to connect the pipe.
Also, with the cooling structure in JP-A-2006-271150, an oil supply pipe must be connected to each end of the motor-generator in the axial direction. In this case, it is difficult to connect the oil supply pipes while checking the seal of each oil supply port. In particular, if a motor-generator is mounted to an electric vehicle and the motor mounting space is set far back and is narrow and there is no work space for an assembly worker on either side in the axial direction of the motor, assemblability of the motor provided with this cooling structure into the vehicle is poor.